Radio transmitter of the kind comprising a magnetron tube energized by a synchronized pulse generator



1956 s. J. HELLINGS ET AL 2,730,621

RADIO TRANSMITTER OF THE KIND COMPRISING A MAGNETRON TUBE ENERGIZED BY A SYNCHRONIZED PULSE GENERATOR Filed Dec. 26, 1951 INVENTORS Simon Jacob Hellings Frunk Krienen B, gbw y United States Patent 1 2,730,621 ADI 1 IEE i- D TCOMPR ING,A M AGNE IRO N TUBE ENERGIZED BY A *SYNCHRONIZED PULSE GENERATOR Simon Jacob l lellin gs and [Frank Krienen, Hiiversum, Nsth anda s q s t H rt WiN Qra Ermk are Trust Company, Hartford, Conn., as trustee Ap iiicauanmsmber"26, 19=s1, sena|Ns. 263,374 Claims priority, application Netherlands January 4, 1951 SClirhs. (ti-1.150

The invention felate s to-radiotransmitters of the kind comprising aniag'iietron tube efie'r'giz ed by a synchronized pulse generator and may particularly 'be used with advan a e-remade uls'e" smitter sgthe magnetrontube "ofwhichgfor ample, "is ehrgizedby pulses of 0.1 to 0.2 ,usec., having a pulse recurrence frequency'of 2000 -c./s. and a--pulse powerof 25 "kw.

' It '-i's-known-to -use in such pulse transmitters a gridcontrolledelectron tube "connected :by'wa'y of a pulse oscillator, the anode and the grid-circuit of this tube being coupled regeneratively by meansof a feed-back transformer, the primary winding of which is included in the anode circuit, while synchronizing pulses are supplied to the control-grid circuit, which includes, also, a delay network determining the duration of the pulses produced and comprising, for exampleyan artificial delay line (line-control blocking oscillator driver). Inknown transmitters comprising such a-pulse oscillator, the pulses derived therefrom control, if'pecessary subsequent to amplification, an electron tube which serves as a switch and which is normally ClltiOflf, this-tube becoming operative each time when a control pulse is received and causing an energizing pulse, the duration of which corresponds with that of the control-pulse, to occur at the magnetron tub'e.

"a basks op de in order avers 'oscillatforyres'idual eurre neph'easmsaa "which' give iise'to overshoot of the rear flank of the enei gizin'gpulse.

The inve'ritioh hasfor its obj'ect t'oirnprov'e and to simplify pulse "transmitters of "thetype'refe'rred to in 'the pr'e arnbl'e e1rrprisin a pul's'e generator, having a T 'd coritrolledelectrontubejconnected by way or pulse *o'sc'iuaten'th *anodeandthe control gr'id circuit of which are regeneratively coupled b'ytlie feedback transformer, the control-grid circuit being coupled with a synchroniz- 're pt11s'e gen'e1-ater-=and"includin a delay "network, which determines the 7 duration of the-pulses produced.

="Ac'cordirig "to-the invention, in'a transmitter of this ki'rid, the-"magrietron tube'isconnectedin parallel with the mary windin'g'of the feedback-transformer and the -gunotion of the nia'guet'ron'cathodeand the primary windingIi's"coupledthrough a coupling capacitor with the tiriodebf the electron tube, this-anode being connected 'throughan irripedanee,preferably an anode resistor, in-

*cluded in the anode-lead to the supply of high anode 'igc nected toa cathode-filament current 'source,-the primary winding of the'transforni'e'r is constructed in a'mann'er otherwise knowh p'er se tobe bifilar and the 'filament of the magnetron cathode-is connected through this bifilar winding to its "source armament current.

In a circuit arrangerrient"according tothe invention it has been found to be particularly advantageous to use'as an electron tube a tubecoiriprising a screen grid "which is located in the shadow of the control-grid as seeenin the'direction of the flow electrons. When the tube is released, the screen-grid thus takes comparatively little current, so'that'with the'use of simple means a high and constant screen-gridyolt'age c'an'b'e maintained-for the duration of the pulses, so that, at complete excitation of theelectron-tube a satisfactory-pulse shape may be obtained.

In order that the invehtibn'rnay be readily carried into effect, anexarhple 'will how'be described in detail with referenceto-the-accompanyingdrawing, which is a circuitdiagram of a radar pulse transmitter representing a preferred embodiment of the invention.

Referring to the "figure, the reference numeral 1 designates a magnetron tube, comprising a cathode 2 provided with-a'filanient wire, and an anode 3. Periodical energizing pulses are'de'rived from an electron tube 4, which is connected by way of a pulse oscillator and which is provided with an earthed'cathode S, aco'ntro l grid '6, a screen-grid 7 and ants-see 8. The said pulse oscillator is made operative by synchronizing pulses from synchroni'zing pulse generator 9.

The-electron tube' i, which is used as a pulse oscillator is normally "cut ofi by means of a negative grid bias voltage of a battery 11 applied to the control-grid 6 through a 'gr'id'res'iston fll. The screen-grid is connected throughascreen-grid resistor 12 to a screen-grid voltage source 13, which is uni-laterally earth'ed. in order to smooth the s'cre'en grid voltage, a smoothing-capacitor 14 is connected between the screen-grid and the earthed cathodeS of the tube-4. The anode 8 of'the tube is connected on the one hand through an anode resistor 15 included intheano'delead'to an earthed-high anode voltage sourcelti and on the other hand through-a storage capacitor 17 to the cathode '2 of the magn'etron'tuhe. The magnetron tube 1 is-connected inp'arallcl with the primary winding'of a feedback transformer 19, of-which the secondary winding 2E is included in the control-grid circuit of the 'electrontube t. The primary winding 18 is bifilar, as is indicated by turns 18 and 38', in order to supply the filament voltage from the filament current source 21 to the filament -22, connected unilaterally to the cathode 2 of the magnetron tube. The turns 18 and llfiare coupled at the ends, as far as high-frequenc currents are concerned, by capacitors 27 and 28.

The control-grid circuit of the electron tube includes not only the aforesaid'secondary winding of the feedback transformer 20 but also a delay network, which comprises various sections and which is of known construction, comprising longitudinal inductors 23 and transverse capacitors 24'. This delay network is connected to one of the output leads of the synchronizing pulse generator 9, of which the other output lead is earthed. An input resistor 25 of the control-grid'circuit of the'electron tube '4 is connected between the output terminals of the synchronizing pulse generator 9.

The circuit-arrangement described above operates as follows:

In the interval between two synchronizing pulses which have, for example, a duration of 0.2 sec. and a recurrence frequency of 2000 c./s., the storage capacitor 17 between the'inagnetro'n cathode 2 and the anode 8 of the "electron tube"' i"-is charg'ed "through the" primary winding 18 of the feedback transformer, operating as a charging choke for the storage capacitor, and through the anode resistor 15 up to the full voltage from the high anode voltage source 16 of, for example, 5 kv. At the occurrence of a synchronizing pulse across the input resistor 25 of the control-grid circuit of the electron tube 4, this synchronizing pulse is transmitted practically without delay via the input capacitor of the delay network 23, 24 and the secondary winding 20 of the feedback transformer to the control-grid 6 of the electron tube 4. The initial blocking of the electron tube 4 owing to the grid bias voltage applied through the grid resistor 10 is obviated by the synchronizing pulse and the tube 4 takes anode current, with the result that the potential of the anode 8 decreases. Then a discharging current of the storage capacitor 17 occurs through the primary winding 18 of the feedback transformer, which results in a further increase in the control-grid potential of the tube 4. Owing to the regenerative feedback between the anode circuit and the control-grid circuit the electron tube 4 rapidly becomes conductive, as soon as a synchronizing pulse occurs, whilst irrespective of the further course of the synchronizing pulse, the control-grid has a strong grid-current control owing to the energy derived from the anode circuit of the tube through the feedback capacitor, which is required to obtain a very low internal resistance of the tube 4. As soon as grid-current occurs, the delay network 23, 24 begins to charge itself, the capacitors 24 of this network having been initially charged by the bias control-grid voltage source 11. This charging current produces a voltage Wave propagating in the delay network and being reflected without reversal of polarity at the open end remote from the synchronizing pulse generator 9, towards the input side, where it produces an abrupt increase in the negative voltage across the input capacitor of the delay network. This abrupt increase in capacitor voltage is transmitted through the secondary winding 20 to the control-grid 6 of the electron tube 4 and produces a potential decrease at the control-grid, which results in an abrupt cut-off of the tube 4 owing to the regenerative coupling of the anode circuit and the control-grid circuit. The period of conductivity of the electron tube 4 is thus accurately determined by the time lag of the delay network 23, 24.

During the period of conductivity of the electron tube 4 the storage capacitor 17 is discharged through the tube 4 and the magnetron tube, which is connected in parallel with the primary Winding 18. The power supplied to the magnetron tube is the higher, the lower is the internal resistance of the electron tube 4 for the period of conductivity, so that it is preferred to use a screen-grid in the electron tube 4, this grid being located to the flow of electrons in the shadow of the controlgrid 6. The tube being conductive, such a screen grid takes a comparatively low current, so that it is possible to keep the screen-grid voltage prevailing during a pulse substantially constant with the use of simple means, in this case a smoothing capacitor 14 of comparatively low value. This favours a suitable pulse shape and permits such an excitation of the electron tube 4 that during a pulse the anode potential becomes considerably lower than the screen-grid potential.

It is not only required to maintain a suitable screengrid voltage during the pulses, but, in order to obtain a low internal resistance of the electron tube, when it becomes conductive, it is also required for the controlgrid potential to be materially higher, during a pulse, for example 30 to 50 v. than the cathode potential. The energy required for such a strong control-grid current for the tube 4 is derived in the circuit-arrangement described above from the anode circuit and not from the synchronizing pulse generator 9, so that the latter is only slightly loaded.

As stated above, the electron tube 4 is very rapidly cut otf at the end of an energizing pulse owing to the regenerative feedback. Since at the occurrence of the rear flank of an energizing pulse both the tube 4 and the magnetron tube 1 are cut off, the magnetic energy then still prevailing in the circuit will give rise to the occurrence of oscillatory residual current phenomena.

These phenomena may be utilized to sharpen the rear flank of the energizing pulse by taking care that the primary transformer winding 18, together with its parasitic parallel capacity forms an oscillatory circuit having a tuning frequency equal to the reciprocal value of about twice the pulse duration determined by the delay network 23, 24. The oscillatory residual current phenomena furthermore give rise to overshoot of the rear flank of the energizing pulses, which is only permissible to a small degree. It has been found that disturbing overshoot of the rear flanks may be avoided in the circuitarrangement described above by using a parallel combination of a damping resistor 26 and the secondary winding 20 of the feedback transformer. The use of a back stop diode, which is, of course, more costly, appeared not to be required.

A tested experimental circuit-arrangement Was as follows: Tube 4: two tubes of the type Philips QQE 06/40 in parallel combination.

Direct supply voltages:

11: vs. V13 500 vs.

V16=+5500 vs. Transformer 19: provided with an E core. L18=L18:25 turns, 1300 ,uh. L20:10 turns, 68 ,uh. Synchronizing pulses: 0.2 ,usec., vs., 2000 c./s. Output pulses: 0.1 ,usec., 2000 c./s. Maximum power: 25 kws.

With the use of a minimum number of components in the circuit-arrangement described above as compared with known circuit-arrangements satisfactory results have been found to be obtainable. The shape of the energizing pulses supplied to the magnetron tube appeared to be very satisfactory for practical uses and the snychronizing energy required is small. A further advantage of the circuit-arrangement described above is that the interval between the front flanks of the synchronizing pulses and the front flanks of the energizing pulsese at the magnetron tube is very small, i. e. about 0.03 nsee, whilst furthermore this interval appeared to be very constant so that a disturbing so-called pulse jitter does not occur.

Furthermore only during an output pulse, a high voltage occurs across the feedback transformer 19, so that the latter may be extremely small sized, under consideration of the normal insulating requirements.

What we claim is:

1. A. transmitter comprising a pulse generator including an electron discharge tube having a cathode, a grid and an anode, an anode resistor, means to apply a positive operating potential to said anode through said resistor, a feedback transformer having a primary and a secondary, a storage capacitor connecting one end of said primary to said anode, the other end of said primary being connected to said cathode, a delay network for determining the duration of the generated pulses, and means coupling said secondary between said grid and cathode through said delay network; means to apply synchronizing pulses to said grid to control the recurrence rate of said generator; and a magnetron having an anode connected to said one end of said primary and a cathode connected to said other end of said primary.

2. A transmitter, as set forth in claim 1, wherein said magnetron is further provided with a filament and wherein said primary of the transformer is bifilar, and including means to supply energizing current through the bifilar Winding to said filament.

3. A transmitter, as set forth in claim 1, wherein said primary winding has an inductance which together with its parasitic parallel capacity forms an oscillatory circuit tuned to a frequency equal to the reciprocal value of about twice the duration of said pulses.

4. A transmitter, as set forth in claim 1, further including a damping resistor connected across said secondary.

5. A transmitter comprising a pulse generator including an electron discharge tube having a cathode, a grid, a screen grid and an anode, first and second resistors, an anode voltage source connected at one end to said cathode and at the other end through said first resistor to said anode, a screen grid voltage source connected at one end to said cathode and at the other end through said second resistor to said screen grid, a storage capacitor, a delay line and a transformer having a primary connected at one end through said capacitor to said anode and at the other end to said cathode and a secondary connected at 6 one end to said grid and at the other end through said delay network to said cathode; a synchronization pulse source coupled to said grid to apply control pulses thereto; and a magnetron having an anode connected to said tube cathode and a cathode connected to said one end of said primary.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Hydrogen Thyratrons, by Harold Heins, reprint of article from Electronics, July 1946. 

